In the art of orthopedic surgery, when bones are fractured and/or broken, it is common practice to releasably secure parts and portions of the broken and fractured bones together with specially designed metal hardware and fasteners throughout those protracted periods of time which are required for the bones to mend.
The intramedullary nail structure that I provide is suitable fro use in different bones. For the purpose of this disclosure, I will illustrate and describe it related to the femur bone. The femur is characterized by a central, intramedullary canal that extends throughout the longitudinal extent of the bone. The canal, like the bone itself, has a narrow or small-incross-section, central isthmus portion and large-in-cross-section, longitudinally outwardly divergent, upper and lower end portions.
The femur is a major load-supporting bone which, in use, is subjected to substantial axially-directed compressive loading and is subjected to frequent and substantial torsional loading.
When femurs are fractured and/or broken to an extent that they cannot be effectively immobilized or restrained from excessive movement to enable proper mending thereof by external means, such as casts and the like, it has become common practice to support those bones with elongate, intramedullary rods. The rods are entered into the intramedullary canals through access openings established in the upper ends of the bones. The rods are driven into the bone to extend from one end portion thereof to the other.
To assure that the rods afford maximum and effective support for the bones, they are often fluted longitudinally so that flutes engage the central or isthmus portions of the bones and set the bones against circumferential movement about the exterior of the rods. When the central portions of the bones are in supported engagement with the rods, the rods are most effective to torsionally immobilize parts and portions of the fractured bones which are in supported engagement with the rods and to assure proper mending of the bones. The upper and lower end portions of the rods extend freely through the upper and lower portions of the intramedullary canals of the bones and afford no radial or lateral support for those portions of the bones. As a result, such rods afford little support and are often of marginal effectiveness in the case of breaks and fractures in the upper and lower (one-third) portions of the bones. The above-referred-to prior art rods are not intended and are such that they afford little or no compressive forces directed longitudinally of their related bones.
A newer class of intramedullay rods address and fasten to the proximal and distal end portions of the medullary canals of related bones. Those rods are typically provided with strut-like blades at their lower distal ends. The blades are deployed radially outward relative to the rods to extend through the large lower end portion of the intramedullary canals and to establish anchoring engagement in and with the lower end portions of the bones, after the rods have been positioned within the bones. The upper ends of such rods are commonly fastened to the upper end portions of the bones by anchor screws that are engaged and extend transversely through the rods and their related portions of the bones.
This new class of intramedullary rods are most often tubular parts with extremely this walls and are highly subject to being torsionally deflected to an extent that they are rendered inoperable. Certain of those thin-walled parts are formed with longitudinally-extending slots and the like that further weakens them and in which boney debris tends to collect and works to fowl operation thereof and impede deployment of the blades.
In addition to the above, the deployable blades that the prior art has provided to anchor the lower end of intramedullary rods to related bones are, for one or more obvious and apparent reasons, unstable and such that they afford rather limited and often times inadequate resistance to torsional turning of the rods within and relative to the bones. The above-referred-to prior art blades are, in some instances, established by long, thin, longitudinally-extending, radially-outwardly-deflectable portions of the rods that are deployed by setting tools engaged within the rods and which, upon longitudinal shifting thereof, displace the blades outwardly. Such radially displaced or deflected blades afford little or no torsional support between their related rods and bones. In other instances, due to the limitation of space, the blades must be made so small, thin, light and/or fragile that they cannot be made sufficiently strong and stiff to prevent excessive torsional deflection and/or movement between the blades and their related rods, resulting in excessive torsional movement between the rods and their related bones and detrimental torsional movement and displacement of the fractured bone parts.